The present invention covers a hydraulic rotary driver or screw apparatus with a preset starting torque and a screw shaft, which is connected to a hydraulic motor, to screw a tool, and accommodated within a cylinder. The shaft is driven up to the preset lower torque with higher rotational speed and, after attaining this torque, is automatically coordinated with a further drive element, which drives the screw shaft via a rotary motion transmitting device with higher torque and lower rotational speed.
The assembly of screw connections, particularly in mass production, must make use of handy, fast, and reliable screw tools. Due to the dynamic effects on screw joints, factors come into play in connection with driving tools which may considerably affect the result of the union. Not only the time-dependent starting characteristic of the screw tools, but also the starting angle up to attaining the initial stress forces are important characteristic values.
Pressure medium driven rotary drive tools have been disclosed in German Publication DT-OS 2 213 549 where the screws are initially tightened in two stages by means of an adjustable pre-torque, and then in addition rotated by an adjustable angle value. A two-stage rotary motor is arranged within the screw tool casing. The rotatable casing is connected to another auxiliary motor which helps turn the casing by adjustable angle values. The auxiliary motor to turn the casing is arranged either coaxially with the principle motor or tangentially with the casing.
Furthermore, a screw tool executed as a hand tool has been disclosed in German Publication DT-OS No. 2 316 560 which is equipped with a pressure fluid motor. The motor driven secondary drive shaft, which is fixed to a screw tool, is driven up to a certain torque via an overload clutch detachable by an axial switching movement. Upon attaining this predetermined torque the shaft is driven via a planetary gear and override clutch. The axially movable part of the override clutch is connected with a part of a power cylinder which is charged with pressure when releasing this clutch and which maintains the clutch in released position.
Also, a screw tool has been disclosed in German Publication DT-OS No. 2 508 971 which is provided with an operating cylinder chargeable by a hydraulic medium under pressure. This cylinder is, on one side, hinged at a counterbearing and, on the other side, it acts upon a segment plate rotating on an axis. The operating cylinder is provided with projections engaging with slots arranged in the segment plate. The segment plate, and thus the axle as well, to which a box wrench for the screw union to be tightened may be connected, can then be further rotated, slot by slot, by the engaging projection movable by means of the operating cylinder. This screw tool is used mainly for assembly, maintenance, and repair of large machines with screws of large diameter.
The above mentioned screw tools described are all of a rather complicated construction, and are, accordingly, large and involved and, particularly with smaller pitch circles of the screws--not usable in other applications for screw tools. Furthermore, DT-OS No. 2 500 679 discloses a rotary driver of common design driven by a hydraulic motor, where the required torque is set by means of a pressure check valve.
The invention relates to a hydraulic screw tool or driver of the above mentioned kind eliminating the disadvantages stated, and having a simplified, compact structure. The compact construction is, in particular, to facilitate its use as a screw tool having multiple uses. To this end, the screw tool, equipped with a high-speed gear, is to guarantee exact tension of screws with a preset starting torque and/or rotary angle. Finally, the device has a low energy requirement compared to the existing screw tools of this type.
Rotary drives operated by pressure medium have been disclosed in DT-AS No. 1 576 142 where one cylinder houses an axially movable piston chargeable from both sides. The two front walls of the piston are provided with pins, each provided with a thread. The two threads have opposite convolutions, whereby one thread cooperates with a corresponding inner thread provided in the cylinder, and the second thread with a corresponding thread arranged at the driven pin. With this arrangement, the axial movement of the piston is transformed into a rotary movement of the driven pin. The driven pin rotates around double the turning angle around which the piston rotates. One rotation of the driven pin in both rotary directions requires identical forces. This rotary drive, however, cannot simply be used for a screw tool, as it does not operate with differential rotary speeds and torques required for the individual phases of tightening screws.
The drawing shows an example of the object of the present invention.